Community Chosen Answer

Be advised that the OS_INSTALLED_DATE may depend on how you setup your machines. If you are performing a scripted install, then it should be accurate. If you are using an image, then I believe it will show the date that the OS was installed on the machine that was used to create the image.

OS_INSTALLED_DATE will show the correct install data on a imaged machine as long as the image is properly sys-prepped. Also another thing to know that with Windows 10 when a machine upgrades from like 1709 to 1803 the install date will change to the date of that upgrade not the original 1709 install which makes sense as that really is a new OS being installed.